1. Field of the Invention
The present invention relates to a mobile telecommunication of third generation, and more particularly, to a method for transmitting a transport format combination indicator (TFCI) inserted to each time slot of a radio frame in a mobile telecommunication system using a W-CDMA standard.
2. Background of the Related Art
In general, the Third Generation Partnership Project (3GPP) group describes a definition of a physical channel of an upward link and a downward link of radio access network. Of the physical channel, Dedicated Physical Channel (DPCH) generally comprises three-layer structure of super frames, radio frames and timeslots. The DPCH has two types. The first type is a Dedicated Physical Data Channel (DPDCH) for transferring dedicated data, and the second type is a Dedicated Physical Control Channel (DPCCH) for transferring a control information.
FIG. 1 shows a data structure of the upward link DPCH according to the standard of 3GPP Radio Access Network (RAN), and FIG. 2 shows a data structure of the downward link DPCH.
Referring to FIGS. 1 and 2, the DPCCH is provided with a TFCI field in each time slot of the radio frame. The TFCI bits are coded and inserted in each radio frame. In other words, information on a transmission format is coded and inserted into each radio frame. A coding of the TFCI bits according to the current 3GPP standard will now be explained herein below. The number of TFCI bits is variable from the minimum 1 bit to the maximum 10 bits, and the number of bits is determined from the point of time when a call starts by means of a signal processing of upper layer.
Different coding methods are applicable to such a TFCI. In other words, when the number of TFCI bits is less than 7, a bi-orthogonal coding, which is a first order Reed-Muller coding, is applicable. When the number of the TFCI bits is greater than 6, a second order Reed-Muller coding is applicable.
According to the current 3GPP standard, the coded sub-code once again undergoes a puncturing so as to generate a code word of 30 bit length.
For example, when the number of TFCI bits, which was determined by upper layer signaling, is less than 7, a TFCI code word is outputted through a bi-orthogonal coding. A (32, 6) coding is applicable to the bi-orthogonal coding. For that purpose, if the TFCI consists of less than 7 bits, a padding procedure is first undergone to supplement the deficient bit value with 0″ from the Most Significant Bit (MSB).
The TFCI code word is inserted into each time slot of a radio frame by two bits. But, the entire length thereof is restricted to be 30 bits. Accordingly, the TFCI code word of 32 bits, which has undergone the bi-orthogonal coding, is punctured as much as 2 bits and inserted into each time slot.
For another example, because the number of TFCI bits determined by upper layer signaling is not more than 10, a TFCI code word is outputted through a second order Reed-Muller coding.
A (32, 10) coding is applicable to the second Reed-Muller coding. For that purpose, if the TFCI bits are less than or equal to 10, a padding procedure is first undergone to supplement the deficient bits with 0″ from the MSB.
The Reed-Muller coded TFCI code word is referred to as a sub-code. The sub-code is punctured by two bits so as to generate a TFCI code word of 30 bit length. FIG. 3 is a block diagram illustrating a channel coding process with respect thereto.
The code word of 30bit length generated as described in the above is divided into fifteen double bit and inserted into each time slot for transfer.
FIG. 4 is a diagram showing insertion of the generally coded TFCI code word into each time slot.
FIG. 5 is a diagram illustrating an encoding structure for generating a (30, 10) TFCI code word.
Referring to FIG. 5, the TFCI bits variable from the minimum 1 bit to the maximum 10 bits are inputted to an encoder. The inputted data bit is lineally combined with 10 basis sequences.
The basis sequences (32 element vectors) used for the linear combination are comprised by a uniform code, in which all the bit values are 1″; five orthogonal variable spreading factor codes represented by (C32, 1, C32, 2, C32, 4, C32, 8, C32, 16) as shown in Table 1; and four mask codes represented by (Mask 1, Mask2, Mask3, Mask4) as shown in Table 2. Said four mask codes arc used to increase the number of code word by 16 times in the conventional second order Reed-Muller coding.
TABLE 1C32,100000000000000001111111111111111C32,200000000111111110000000011111111C32,400001111000011110000111100001111C32,800110011001100110011001100110011C32,1601010101010101010101010101010101
TABLE 2Mask100101000011000111111000001110111Mask200000001110011010110110111000111Mask300001010111110010001101100101011Mask400011100001101110010111101010001
However, the TFCI encoding according to the conventional technology as described above poses the following problems.
When two bits are punctured to generate a (30, 10) TFCI code word, which is inserted in the time slots and transmitted to the actual TFCI field from the (32, 10) code word, a minimum hamming distance loss is up to 2 at a maximum basis. Also, when a (16, 5) code word is punctured one bit to generate a (15, 5) TFCI code word, the maximum hamming distance loss is occurred in that case as well.